No description available.

No description available.

This study was restricted to birds using tree-holes as nest-sites. Of a total of 20 species in the study area, only 13 were sufficiently abundant to merit consideration. These fell into three natural groups on the basis of hole size, with only one euryoecious species (Iridoprocne bicolor) nesting in all three groups. Only the group based on holes made by the Colaptes woodpeckers (Flickers) can presently be construed as showing evidence of nest-site competition. Physical and ecological characteristics of nest-sites are analyzed in terms of intensification or amelioration of nest-site competition. The competing species, all using holes made by Colaptes cafer, are Sturnus vulgaris, Sialia currucoides, Bucephala albeola, Iridoprocne bicolor and Falco sparverius. The data suggest that although competition is now present in this group, it may have been absent before the advent of Sturnus in the avifauna. Neither selection for different sites nor competitive exclusion seem to have occurred before the appearance of Sturnus, which now occupies roughly 25% of all available nests, but one or both of these may now be going on. / Science, Faculty of / Zoology, Department of / Graduate

No description available.

This study relates the species composition, numbers, and habits of a hole-nesting avifauna to its environment in successional stages of a coniferous forest in southwestern British Columbia. Emphasis is placed upon explaining an observed presence or absence of nest-site competition. In two breeding seasons, the hole-nesting avifauna was found to be low in numbers of both species and individuals. Most of these birds were able to excavate their own nesting cavities, and commonly did so, for which activity the habitat generally provided ample opportunity. As the species present often differed widely from one another in the type and placement of their preferred nest cavities, there was usually a surplus of different cavity types present. Secondary hole-nesters either concentrated their activities around the buildings in the nearby town, neglecting the more "natural" sites available; were not obligated to use cavities when nesting; or occurred in such low densities, and were so positioned in the available suitable habitat, as to suggest that nest-site competition had no effect upon the populations. Only scattered indications of nest-site competition were observed in wooded areas. Four species nested in crevices in buildings and in bird boxes in a small town, where their breeding population densities were much higher than in the surrounding countryside. Nest-sites were judged to be present in excess, and nest-site competition, observed infrequently, was so rare, and apparently without significant harmful effects, that it was judged to be of negligible importance as a population-regulating factor. The overall absence of nest-site competition is contributed to not only by the preferences of the species regarding their nest-sites, but also by the fact that the results of their habitat selection processes, and their living habits within these habitats, tend to keep them ecologically distinct. / Science, Faculty of / Zoology, Department of / Graduate

Eighty-three species of vascular plants were inventoried on the prairie relict during peak dickcissel nesting. Based on foliar cover and occurrence frequency, the five dominant plants were heath aster (Aster ericoides), eastern gammagrass (Tripsacum dactyloides), little bluestem (Schizachyrium scoparium), sensitive briar (Schrankia roemeriana) and meadow dropseed (Sporobolus asper). Sixty-one percent of dickcissel nests were constructed on or immediately next to three plant species: eastern gammagrass, sensitive briar and green milkweed.

No description available.

Nest and perch locations of Black-throated Blue Warblers in West Virginia, Virginia, and New Hampshire were examined to determine the structural similarities of the vegetation surrounding these sites and to determine the contribution of each location to the description of the territory. Principle component analysis (PCA) was used to determine habitual variables correlated with the location of the nest and perches. Factors derived from the analyses were combinations of either macro or microhabitat subsets of vegetational variables. In the nest site analysis, four macrohabitat factors described the presence of major tree species, along with structural characteristics of the overstory and understory. The interaction of overstory and understory was expressed by the density of vegetation in various layers in the nests. The 4 microhabitat factors were concerned with structures within 1 meter of the nest. Pattern analysis of vegetation structure suggests nest site placement depends on the layering of a discrete overstory and on a particular subset of structural variables which are present in the understory across habitats. Principal component analysis of perch data produced a set of 4 factors describing the contribution of macro and microhabitat variables. Microhabitat factors were highly correlated with the variables DISTANCE FROM TRUNK, LENGTH OF BRANCH, SIZE OF BRANCH, and PERCH HEIGHT. The most strongly correlated macrohabitat variables were BIRCH IMPORTANCE VALUE and % CANOPl COVER. These data indicate males are located at the lower edge of the canopy in mature forests in areas relatively free of understory. Comparison of these data with similar variables measured at nest sites showed male perches are not correlated with nesting locations. In addition, the variation in habitat models based on perches was twice as large as models based on nest sites. When male Black-throated Blue Warblers obtain a territory, habitat is incorporated which is used by the female for nesting, but not by the male for singing or foraging. These nesting sites have less variation in the vegetation surrounding them than perches utilized by the males. / Ph. D.

No description available.

No description available.